The present invention relates to an adhesive film for semiconductor, a lead frame and a semiconductor device using the adhesive film for semiconductor, which adhesive film can be easily peeled off from lead frames and sealing resins, contributing to high working efficiency in the production of packaged semiconductor devices. The present invention also relates to a method of producing a semiconductor device.
Conventional packaged semiconductor devices have been produced by bonding a semiconductor element to a die pad of a lead frame with an adhesive such as a silver paste, connecting it with the lead frame by wire-bonding and then sealing the whole body except outer leads for external connection. However, with a recent demand for packaged semiconductor devices of higher density and smaller area and thickness, packages of various structures have been developed. Some examples are LOC (lead on chip) and COL (chip on lead), but are not decreased enough in area and thickness.
Another approach developed to solve these problems is a package structure wherein only one side of packages (the side bearing semiconductor elements) is sealed to use the exposed backside of lead frames for external connection. Packages of this structure achieve the decrease in area and thickness because lead frames do not protrude from sealing resin, but the sealing resin tends to creep even on the backside of lead frames.
The inventors have found that such a trouble might be prevented by protecting the backside of lead frames by bonding an adhesive film and peeling it off after sealing. This method needs an adhesive film which has enough bonding strength to lead frames and, after resin sealing, can be peeled off easily with heat or the like. However, there has been no adhesive film for semiconductor that possesses both the antipodal properties.
An object of the present invention is to provide an adhesive film for semiconductor and a lead frame and a semiconductor device using the same, which adhesive film not only has enough bonding strength to lead frames and, after resin sealing, can be easily peeled off, but also possesses other characteristics necessary in semiconductor applications.
Another object of the invention is to provide a method of producing semiconductor device whereby semiconductor devices of high density and small area and thickness can be produced efficiently.
Accordingly, the present invention relates to an adhesive film for semiconductor, which comprises at least one resin layer A, and, after bonded to a lead frame, has at 25xc2x0 C. a 90xc2x0-peel strength of at least 5 N/m between the resin layer A and the lead frame, and, after a lead frame is bonded to the adhesive film for semiconductor and sealed with a sealing material, has at least at one point of temperatures ranging from 0 to 250xc2x0 C. a 90xc2x0-peel strength of at most 1000 N/m between the resin layer A and each of the lead frame and the sealing material.
According to the present invention, after the sealing with the sealing material, the adhesive film for semiconductor preferably has at a temperature ranging from 100 to 250xc2x0 C. a 90xc2x0-peel strength of at most 1000 N/m between the resin layer A and each of the lead frame and the sealing material.
According to the present invention, it is preferable that the adhesive film for semiconductor has a 90xc2x0-peel strength of at most 1000 N/M between the resin layer A and each of a lead frame and a sealing material at a temperature at which the adhesive film for semiconductor is peeled off from the lead frame and the sealing material after sealing with the sealing material.
According to the present invention, the resin layer A preferably has a glass transition temperature of 100 to 300xc2x0 C. Further, the resin layer A preferably loses weight by 5% by weight at a temperature of 300xc2x0 C. or higher.
According to the present invention, the resin layer A preferably has an elastic modulus of at least 1 MPa at 230xc2x0 C. Further, the resin layer A preferably comprises a thermoplastic resin having an amide group, an ester group, an imide group, an ether group or a sulfone group, particularly preferably an amide group, an ester group, an imide group or an ether group.
The adhesive film for semiconductor of the present invention preferably has a support film with one or each side coated with the resin layer A.
According to the present invention, the support film is preferably made of a material selected from the group consisting of aromatic polyimide, aromatic polyamide, aromatic polyamideimide, aromatic polysulfone, aromatic polyether sulfone, polyphenylene sulfide, aromatic polyether ketone, polyallylate, aromatic polyether ether ketone and polyethylene naphthalate.
The adhesive film for semiconductor of the present invention preferably has a ratio of a thickness (A) of the resin layer A to a thickness (B) of the support film, (A/B), of at most 0.5.
According to the present invention, it is preferable that one side of the support film is coated with the resin layer A having adhesiveness, and the other side is coated with a resin layer B having no adhesiveness which has an elastic modulus of at least 10 MPa at 230xc2x0 C.
The present invention further relates to a lead frame to which the adhesive film for semiconductor of the present invention is bonded.
The lead frame of the present invention is preferably bonded to the adhesive film for semiconductor, with one side of the lead frame contacting the resin layer A.
The present invention further relates to an adhesive film-bearing semiconductor device using the adhesive film for semiconductor of the present invention.
The adhesive film-bearing semiconductor device of the present invention preferably comprises
the adhesive film for semiconductor,
a lead frame bonded to the adhesive film for semiconductor with one side of the lead frame contacting the resin layer A,
a semiconductor element bonded to a die pad on another side of the lead frame, a wire connecting the semiconductor element and an inner lead of the lead frame, and
a sealing material which seals the semiconductor element and the wire.
The present invention further relates to a semiconductor device produced by peeling off the adhesive film for semiconductor from the adhesive film-bearing semiconductor device described above.
The present invention further relates to a method of producing a semiconductor device, comprising
a step of bonding an adhesive film for semiconductor to a side of a lead frame having inner leads and a die pad,
a step of bonding a semiconductor element to the die pad on the other exposed side of the lead frame,
a step of connecting the semiconductor element to the inner leads with wires by wire-bonding,
a step of sealing the exposed side of the lead frame, the semiconductor element and the wires with a sealing material, and
a step of peeling off the adhesive film for semiconductor from the lead frame and the sealing material.
In the case where the lead frame used in the above method comprises a plurality of patterns each of which comprises a die pad and inner leads, the lead frame is optionally divided into a plurality of semiconductor devices each of which contains one semiconductor element.
In the method described above, the adhesive film for semiconductor is preferably the adhesive film for semiconductor of the present invention, and the adhesive film for semiconductor is bonded to the lead frame, with the resin layer A contacting the lead frame.